Piezoelectric crystal apparatus



March 20, 1945.

l. E. FAIR PIEZOELECTRIC CRYSTAL APPARATUS Filed Dec. 51, 1942 3Sheets-Sheet l INVENTOR l E. F4 IR A 7' TORNE V March 20, 1945. E M2,371,613

PIEZQELECTRIC CRYSTAL APPARATUS Filed Dec. 31, 1942 I5 Sheets-Sheet 3 INl/EN TOR E. FAIR By WM ATTORNEY Patented Mar. 20, 1945 2,371,813PIEZOELEC'IBIO CRYSTAL APPARATUS Irvin E. Fair, Lynllhurst, N. 1.,assignor to Bell Telephone Laboratories,

Incorporated, New

York, N. Y., a corporation of New York Application December 31, 1942,Serial No. 470,759

(Cl. 17l327) 16 Claims.

This invention relates to piezoelectric crystal apparatus, andparticularly to wire support systems for piezoelectric crystal elementsuseful, for example, in oscillation generator systems, filter systems,and in electromechanical vibratory systems generally.

One of the objects of this invention is to prevent wire vibrations inwire-supported piezoelectric crystals from adversely affecting thedesired crystal vibration.

Another object of this invention is to reduce the effects of vibrationsin crystal supporting wires upon the crystal activity and frequency.

Another object of this invention is to improve theactivity and thefrequency stability of wiresupported crystal elements.

In order that a piezoelectric crystal may vibrate freely, it isdesirable that the means used to support the crystal and to maintaincontact with its plated electrode surfaces have a low mechanicalimpedance and at the same time have suflicient rigidity that thecomplete crystal unit assembly when subjected to mechanical shock orother externally applied vibration may not change its characteristics asan oscillator. If a crystal supporting spring wire be fastened orotherwise held against the crystal at any point, the crystal when in anoscillating condition will tend to generate motion in the support wirein contact therewith, and the closer the support wire is placed to thenodal point of the crystal, the less will be the motion generated by thecrystal in the support wire. Accordingly, the crystal supporting wiresmay be placed as close as possible to a nodal point of the crystal andalso so constructed as to have a very low'mechanical impedance at ornear the desired operating frequency or frequencies of the crystal. Atype of support which meets this requirement is that of a thin springwire or rod vibrating in flexure, one end thereof being in effectclamped at or near a wire node and the other end being free to vibratein contact with the surface of the crystal. the length thereof beingsuch that its frequency of antiresonance equals that of the crystal, orapproximately so, so that very little energy from the crystal isrequired to drive the supporting wire. and any energy received by thesupporting wire from the crystal is reflected from the clamped end ofthe supporting wire and thereby kept within the composite vibratingsystem.

In piezoelectric crystal devices of the spring wire supported type suchas, for example, those disclosed in A. W. Ziegler Patent 2,275,122,dated into vibration as a result of the vibration of the crystal elementwhich is suspended by such supporting wires, and the wire vibration mayadversely affect the desired crystal vibrational frequency or render itsluggish in vibration or prevent its operation altogether in some cases.These adverse effects may be the more pronounced where the crystalelement is relatively very small in size or where the supporting wiresare not attached to the crystal element at or very near to a nodethereof.

In accordance with this invention, a wire-supported crystal may beprovided with massed weights or clamps placed on and suspended by thecrystal supporting conductive lead wires, the massed weights being notonly of sufficient mass but also of suitable location with respect tothe nodes of the supporting wires as to prevent vibrations in thesupporting wire system from adversely affecting the activity or thedesired frequency vibration of the crystal element.

In accordance with a feature of this invention, a small solder globuleor ball or other suitable mass may be placed or cast firmly on theflexible spring support g wire or wires at a selected location between te crystal and the far or outermost end of the supporting wire system.More particularly, the small solder ball may be placed at or near a nodeof each supporting wire and away or remote from the loop of motionthereof, the eflective wire length between the crystal element and thesolder ball being thereby made to have a natural frequency which isfundamentally or harmonically related to the desired crystal frequency,and the solder ball being made of a mass sufficient to prevent thecrystal lead wire vibration from passing therethrough to the far or out-.ermost portion of the spring wire support remote from the crystal. Suchsmall weights or loads of metal as lead-in solder balls placed on andsuspended by the crystal supporting wires substantially at a node ofmotion thereof and made of adequate mass will function to reduce dampingand improve the Q and operation of such wire mounted crystals.

For a clearer understanding of the nature of this invention and theadditional advantages, features and objects thereof, referenceis made tothe following description taken in connection I with the accompanyingdrawings, in which like March 3, 1942, the wire support system may beset reference characters represent like or similar parts and in which:

Figs. 1 and 2 are enlarged front and side views respectively of apiezoelectric crystal mounting embodying this invention, Fig. 2 being aview taken on the line 2-2 of Fig. 1:

Fig. 3 is an enlarged detail view showing a support wire attached to thecrystal by means of a solder cone soldered to a baked silver paste spoton the crystal element;

Fig. 4 is an enlarged'detail view showing a spherical solder ballJoining the ends of two wires forming a wire upport for a piezoelectriccrystal device;

Fig. 5 is a greatly enlarged detail view of a crystal supporting wirefastened at one end to motion of the crystal plate I when in operation.

the crystal by means of a bell-shaped solder cone,

' and extending straight through a solder ball to an outer support;

Fig. 5;

Figs. 7,8 and 9 are enlarged view, showing,-

the use of a nodal soldered stirrup as a substitute for the nodal solderball of Figs. 1, 2, 4, 5 and 6;

Fig. 10 is a perspective view of a modification of the crystal mountingshown in Figs. 1 and 2;

.Figs. -11 and 12 are respectively face and end views of a four-wiresupport system as applied particularly to a longitudinal mode typeofcrystal element; and

Figs. 13 to 17 are views showing various modiilcations of the invention.

Referring to the drawings, Figs. 1 and 2 are enlarged front and sideviews. of a piezoelectric.

crystal device comprising a face-mode quartz crystal element I havingopposite, conductive electrode coatings 2 and 8 formed integraltherewith and thickened at the central regions of supv motion prevalent.in quartz crystals are the har- 7 1s Fig. 6 is an enlarged detail viewshowing a modification of the crystal supporting wire oiv the to it and,which may by their presence hinder The etching referred-to should notbeoverdone inasmuch as with too much etching, the silver coatings 2 and!may have a tendency to flake .01! near the edges and corners of thecrystal with a resulting absorption of energy from the crystal plate Iand a decreased Q thereof. When the etching bath is agitated, the timeof etching may be decreased andsome improvement in uniformity ofresonant resistance .may be obtained. Also, the thickness of the crystalplate I may be.

adjusted to a suitable value relative to its major face dimensions inorder to avoid nearby 01' coupled undesired frequencies or modes of.

motion therein, that mayinterfere with the desired resonance. Amongtheundesired modes of monic flexure modes vibrating along the thicknessand propagated along the width'and length of the crystal plate I.Accordingly, the thicknessof the crystal plate I may-be adjustedrelative to the major face dimensions in order to place undesired. modesin regions that do not conflict with the desired main resonantfrequencyor with any desired secondary resonance thereof. f

The crystal coating land 3 may consist of I any suitable conductivecoating such as, for example, a very thin coating of silver applied tothe crystal surfaces by evaporation in vacuum port 4 where twohorizontal or laterally extending supporting fine spring lead wires 6and'l are soldered thereto by means oftwo small solder dots or cones 5.The outer ends of the two horizontal lead wires 8 and I are welded orsoldered by a cast solder ball or other metallic mass ID to the top endsof two supporting upright semicircular spring wires 8 and 9 which may bea part thereof. The lower ends of the wires 8 and 9 are wound around andsoldered to two pin ter minalsl2 of an enclosing container II, which maybe hermetically sealed or evacuated and constructed of any suitablesize, shape and material.

- be of the same or slightly larger diameter, as

may be required to support the crystal element I. It will be understoodthat the crystal element I may be of any type that it may be desired tomount, such as, for example, a quartz crystal element of the face shearmode type having its node or point of minimum motion at or near thecenter of the crystal element. Examples of such face shear mode crystalsare, disclosed, for example, in G. W. Willard United States Paten2,268,365, issued December 30, 1941.

To obtain stability in its resonant resistance,

the bare quartz plate I may be uniformly etched in hydrofluoric acid,for example, to remove any particles of quartz dust left in the smallcrevices 75 of the quartz plate I that are not tightly bonded or byother suitable process. At the points where the lead wires 6 and I areto be attached, a small spot 4 of baked silver paste maybe applied tothe quartz and baked firmly thereon in a known manner. Y shapedbakedsilver paste spot 4 which has been baked onto the quartz crystal Iat ornear a node thereof, a thin electrode fllm 2 or 3 of evaporatedsilver being applied thereover and a lead wire 6 being soldered to thebaked silver paste spot I by means of a smallsolder dot or cone 5. The

leadwire 6 may. haveits end firmly embedded in the solder cone 5, asillustrated in Fig. 3..

For purposes of mechanical strength and electrical conductivity, a goodjoint is needed between the crystal I and the supporting lead wire landalso between the lead wire 6 and the mount wire 8. The silver spot I maybe burnished or' otherwise cleaned in order" to obtain'a clean surfacefor soldering the supporting wire 6 or I thereto. The proper shaping ofthe solder cone 5 results in a stronger joint between. the leadwire 6 orI and the silver spot 4. If the solder cone 5 is made too high and toonarrow, it may under stress at the base thereof pull off from silverspot 4, and if the solder cone 5 is made too lowv in height, astraight-ended lead wired or I may under stress pull out from thesolder-cone 5. Q I If desired, the end of the leadwire 6 or 1 may bebent at right angles, or bent in hook'form-v as illustrated in Fig. 3,in order to prevent it j from pulling out'fromthe solder cone :5. Ifdesired, the soldering may be done by indirecth'eat ing such as by hotair blast or radiated heat, for example, in order to prevent possibledamage to the tal by direct heating I Y The lead wires '5 and I may besoldered to the:

silver spot 4 on the crystalby using a small disc or pellet of solderplaced therebetween and then fused to have the approximate cone or hellshape 7 ,as shown'in Fig. 3. The disc of solder referred to-mayinitially be of about .019-inch diameter d by.0l5-inchthickor'equivalent or other suitable volume, and may becomposed of 40 per cent lead,

Fig-3 is a detail showing a circular stants of the crystal I.

I per cent tin with about 0.1 per cent silver added. The small quantityof silver is added to prevent the solder from absorbing the silver fromthe silver coatings I, I and I. A rosin alcohol flux in the proportion01' 2 grams rosin to I ounces alcohol may be used for soldering. Aftersolder- .ing, a camel's hair brush may be used to wash the solderedJoint with denatured alcohol.

Since the Q or ratio of mass reactance to resistance of ordinary softsolder itself-such as, for example, solder composed of 50 per cent tinand 50 per cent lead is rather low and decreases furth'er with anincrease of temperature, and since the solder dot I occupies a movingarea on the crystal surface and the same type of motion occurs in thesolder I as that of the crystal in contact therewith, the effect of thesolder dot I may be minimized by making it as small as possible and byplacing it as near as possible to a crystal node thereby to minimizeabsorption of energy in the solder with resulting decrease of activityof the crystal I. The effect of the solder dot I on the activity of thecrystal I may also be minimized by using a tin-antimony solder or otherhard solder instead of the ordinary soft lead-tin solder since theformer may have a better Q at the upper operating temperature limits dueto its higher melting point. Accordingly, by using a hard solder suchas, for example, a solder composed of 95 per cent tin and 5 per centantimony, the effect of decreasing crystal activity at high temperaturesmaybe eliminated or reduced. This effect may also be reduced by limitingthe amount of solder I, whether hard solder or soft solder is used. Alead-tin eutectic solder composed of 63 per cent tin and 37 per centlead will permit less solder to be used at the crystal joint I andthereby reduce the amount of coupling to the supporting wire system. Theeffects produced by using different size solder dots I and differentplacement of the lead wires I and I on the crystal can be determined bytheir effects on the con- Typical constants for face shear mode CTcrystals are: ratio of capacities-350 and Q-l5,000 to 30,000. The maineffect of large solder dots I on the crystal is to reduce the Q sincemotion will be transmitted to it from the crystal I. The amount as wellas the shape of the solder I at the crystal will affect the Q of thecrystal I.

Fig. 4 is an enlarged detail showing the use of the spherical solderball II for joining together the two ends of the lead wire I and theupright spring wire I embedded therein. While the supi porting springwires I and I of Figs. 2 and 4 are therein shown in a particularposition, namely, in planes at right angles with respect to thesubstantially coaxial lead wires I and I, it will be understood thatthey may extend from the solder balls II in any direction. Asillustrated in Figs. 1 and 2, the upright spring wires 8 and 9 may havesemicircular, circular or other bends therein to provide a resilientsupport for the crystal element I. As particularly illustrated in Figs.1 and 2, the semicircular springs I and I may be in planes that aresubstantially parallel with respect to each other; or they may beinclined inwardly towards the crystal, or outwardly and away therefrom.The bent portions thereof may be elliptical or semicircular and may beof substantially. the same shape and size having their curved or bentportions extending from the same side of the horizontal coaxial leadwires I and l, as shown in Fig. 1, in order to prevent twisting of thehorizontal lead wires I and 'I soldered thereto, whenever the crystaldevice is subjected to externally applied shock or jar, as may occur,for example, in mobile installations or during trade- 5 flirtation.

Fig. I is a greatly enlarged detail view of the crystal lead wire I or Iarranged to extend straight through the solder ball II, and having abell-shaped solder cone I for fastening the leadwireIorItothecrystalcoatingIorI. This bell-shaped type of solder cone Iallows the lead wire I or I to be twisted in handling without muchdanger to breaking cone I and thereby forming a crater. For the purposeof analysis, the solder cone I is assumed to become part of the crystalI and to move with it, and the length of the lead wires I and Ivibrating in iiexure is computed or determined from the top or apex ofthe solder cone I as described hereinafter. The amount of solder used inthe cone I is kept at a minimum in order that the constants of thecrystal equivalent circuit may not be modified too much by it. Theeffect of the solder in the cone I on the equivalent circuit is to raisethe resistance in the equivalent circuit for the crystal and thisresistance may increase with an increase in temperature. Accordingly.the amount of solder permissible in the cone I is determined by themaximum temperature at which the crystal unit is to be operated and theminimum Q allowable for the crystal unit.

As illustrated in Fig. 5, the lead wire I or I extends straight throughthe solder ball II which is suspended thereby and is attached to thesupport wire I or I by any suitable means such as a solder Joint II.Alternatively, instead of soldering, the lead wires I and I may be spotwelded at II, to the supporting spring wires I and I without softeningthe phosphor bronze lead wires I and I to any appreciable extent. A verytight bond at II is obtained by such spot welding. Also, a solder pelletmay be placed on the Joint II and spot welded at the same time in orderto add weight at the joint II. if it is found necessary to addadditional weight at this joint in order to keep standing waves off themounting spring wires I and I.

Fig. 6 is a greatly enlarged view illustrating another type of crystalwire support utilizing a headed wire at Ia, in place of a solder cone Iof Fig. 5, for attaching the lead wire I or I to the crystal I. Theheaded wire end Ia may be similar to that of an ordinary nail head andmay be connected to the crystal coating I by sweating the wire head Iato the crystal coating I. The wire head In may be a machined part andmay be made of constant or uniform dimensions for many or all types ofmountings. The amount of solder necessary to sweat the wire head Iainthe silver spot I of the crystal I is considerably less than that usedin a solder cone I, and hence the headed wire form of mounting Ia asillustrated in Fig. 6 will have less dissipation of energy at the highertemperatures. Moreover, the coupling between the vibrating system of thewires I and 1 and the vibrating system of the crystal I is reduced bythe use of the headed wire In shown in Fig. 6. This results in reducingwhat may be termed a double system of standing waves on the wires I andI, one resulting from reflections from the solder ball II or clamped endof the wire, and the other resulting from reilections between the two ormore resonant wires I and I coupled through the crystal I. These awaythe top or apex of the.

effects may be reduced by a reduction of the coupling between thecrystal I and the wire vibrating systems 6 and I. It is difllcult if notimpractical to try to balance the solder cones sufliciently to preventthe crystal motion from being transmitted to the lead wires 8, I, 8, 9.In most cases, the considerable amount of crystal motion transmitted tothe lead wires 6, I, 8, 9 may be suflicient to set up standing wavestherein.

Instead of using the integral form of headed wire 5a, the nail head formof Fig. 6 may consist of a metal washer having a small central openingof about the same size as the outer boundary of the wire 6 or I, thewasher opening being placed'on the extreme end of the wire 6 or I andsoldered both to the wire 6 or 1 and crystal coating 4 at the same time.By proportioning the thickness and the diameter of the washer, thejoints between the wire and washer and between the washer and crystalplating may be made to have the same strength. If desired, the-washermay be stamped cone-shape, the larger diameter of the cone being placedat the jointbetween the washer and the crystal plating 4.

' As stated hereinbefore, the ends of the support wires 6 and I attachedto the crystal I move with the crystal motion at the region ofattachment, whether a shear, longitudinal, flexure or other type offace-mode or thickness-mode vibration is employed in the crystal I.

The effect of the wire support system on the crystal frequency may bereduced by increasing the size of the crystal element I, thus increasingthe ratio of mass of the crystal I with respect to the mass of the wiresupports. In the case of face-mode crystals the frequency of which isdetermined mainly by the major face dimensions, the thickness dimensionmay be conveniently increased in order to increase'the crystal massrelative to the supporting wire system. Since in practice the lead wires6 and I are not ordinarily attached to the crystal exactly at a nodalpoint thereof, some of the motion of the crystal I is imparted to thelead wires 6 and 1 which support the crystal I, and the lead wires,therefore, become a part of the mechanically vibrating system. If thelead wires 6 or I' should be terminated at or too near a loop or pointor maximum motion thereof, such as multiple half wavelengths of thedesired'crystal frequency, a high mechanical impedance would bepresented at the point of contact 5 between the crystal I and the leadwires 6 and I, which would tend to prevent motion of the crystal I andabsorb energy from it with resulting increased resistance at resonance,and where there are several supporting lead wires on the crystal I,considerable energy may be absorbed from the crystal I.

It is possible to damp or dissipate the motion in the wires 6, I, 8, 9by placing thereon along the entire lengths thereof some clamping ordissipative medium such as, for example, rubber cement, cotton sleeving,gold or other soft metal plating or other viscous material. Suchdissipative media on the supporting lead. wires may be used to improvethe activity. of the crystal I, but at the same time they tend to reducethe springiness of the lead wires 6, I. Alternatively,

instead of using such dissipative media, the crys-.

tal activity and stability may be improved by using a properly placedsingle massed weight III on each of the lead wires 6 and I in order toreflect, rather than to dissipate, the wave motion therein. By the useof such weights I0, harmful vibrations in the crystal supporting leads6,

amount of motion in the lead wires 6 and I, and

I. 8, 9 connecting the crystal I with the mounting posts I2 may beeliminated by compelling the lead wires 6 and I adjacent the crystalplating I to vibrate in eflect as a clamped-free bar between the weightsIII on the lead wires and the crystal l. The weights III may consist ofany suitable massed weight fastened to the lead wires 8 and'lat a properpoint thereon. The proper point is at or near the wire nodal point orthat at which the portion of the lead wires 6 and I between the solderdot 5 on the crystal I and the weight I0 acts as a clamped-free bar inresonance to the motion transmitted to the wires 6 and I by the crystalI. tions of the lead wires between the weight Ill and its far ends I2may be bent or mounted inany' manner without affecting the activity orfredamping is introduced into the crystal I when the weight In is placedat or near one of the wire nodal points. The weights I0 may be placedoil the wire nodal points up to about a quarter of the distance betweenthe nodes providing the motion transmitted to the wire 6 or I is not sogreat as to effect too much damping of the crystal I. Theallowablevariation in any case depends upon the the size of the crystalI relative to its supporting wire system.

When the solder mass III is substantially nod-- ally located on thesupport wires 6 and I and is of sufiicient mass relative to the supportwires, the support wires 6 and I between the mass Ill and the crystalelement I become a composite vibrator at the crystal frequency and thesupport wires 8 and 9 between the solder mass I0 and the fixed base I2do not afiect the crystal vibration adversely. Loads I0 so placed on themount. wire system of the crystal I preserve high crystal activity orhigh Q," and low activity of the crystal I resulting from couplingbetween the vibrating wire supports and the crystal I may be avoided.The procedure of placing the weights III at the nodal regions on thewire supports controls, the mechanical coupling between the crystal andthe crystal supporting wire system. The mass I0 is added at a specifieddistance along the lead wires 6 and I on both sides of the crystal I tocause reflection of the flexure vibrations produced on the lead wires 6and l by the crystal I when it is operated. The distance is selected tocause maximum output in the crystal oscillator unit. The solder balls IDare placed on the lead wires 6 and I at or near a node thereofcorresponding to the frequency of the crystal. Since in most cases thesolder ball I0 need not be exactly at a node of the lead wires, the wirelength between the solder ball l0 and the crystal element I may be afixed value representing a. compromise suitable for use with crystals ofdiilerent frequencies but which are not too widely diiferent infrequencies.-

The small balls of solder III are placed ,41, 4,

'54, etc. of a wavelength of the waves produced on f the lead wires 6and I from the top or apex of the solder cone 5. Depending upon theparticular design, the solder balls Ill may be about .060 inch indiameter or of other suitable value-to give a mass sufllcient to preventmotion on the outer support wires 8 and 9 from adversely affecting thecrystal vibration. When such solder weights The remainingporilareusedonandsuspendedbythewirest and I, theends of-the lead wires 8and I beyondths weights Il may be soldered to the supp t at any pointwithout aifecting the crystal resonant frequency or activity. The sizeof' the solder ball weight II is determined just sumcient to preventvibration from the crystal I from being transmitted past the weight It.This allows the support to be fastened at any point on the wire supporton the side of the weight II away from the crystal I.v The weight forone particular case was about 1.5 milligramsv of solder. Only a smallamount of mass II is n and where the mam II is adamped material suchas alead-tin solder, there will be little or no motion of the wires outsidethe load points Ill. Any suitable means may be employed to space andplace the nodal solder ball II at a given distance from the crystalsurface.

Accordingly, with the lead wires 6 and I soldered onto the crystalplatinss 4, each soldered Junction itself mova and generates atransverse wave in the lead wires 6 and I, the motion being roughlyindicatedby the dotted line in Fig. 5. -When the leadwire i or I issoldered by the solder ball II at a point corresponding to a nodal pointon the lead wires t and I, there is no adverse reaction on the crystal.But ii' the lead wire 6 or I should be soldered at a point B, which is aloop or point of maximum motion in the lead wire I or I, the effect isto offer a high mechanical impedance at the point of contact I with thecrystal I which would be reflected as a lowering of the activity of thecrystal I. The nodes and loops on the lead wires 6 and I may bedetermined by trial, as by using a fixed clamp support on the lead wires6 and I at various distances from the crystill I. When the clamp occursat a loop of motion in the lead wire 6 or I, the oscillator activity maydecrease to zero. The effects of clamping the lead wires 6 and I overwide ranges around the wire nodes thereof is to give a change in crystalfrequency, the amount of which will be determined by the couplingbetween the lead wires 6 and I and the crystal I. A clamp or weight IIIplaced at or near a node of motion on the lead wires 6 and I gives goodactivity for the crystal unit and stabilims the frequency.

The motion in the lead wires 8 and I is roughly that of a round rodvibrating in clamp-free fiexure. However, this is not strictly a case ofpure clamp-free eflfect, since the point of contact 5 with the crystalI, which is the assumed free end, is restricted to a small slope, andthe other end at the solder ball II is more of a yielding typesupportthanafixedtypeof clamp.

The frequency f of a spring phosphor bronze clamp-free long rod or wirevibrating in flexure is given by the equation:

where v=transmission velocity of longitudinal waves in centimeters persecond d=diameter of rod in centimeters or the direction of particlemotion l=length of rod in centimeters or direction of Propagationm=l.875 for the first fiexure mode; and

=(n%)r for the second, third, etc. fiexure mode where n is the numericalorder of the mode of vibration as 2.3, etc.

From Equation 1, the length of a given rod or wire at a given frequencymay be computed.

As an example, assuming a' loo-kilocycle per second crystal I using aspring phosphor bronze wire rod of I millimeter in diameter, the lengthl of such clamp-free wire rod for the first mode will be and for thesecond mode will be l=.567 centimeter. 4

As another illustrative example for a phosphor bronze lead wire I or Iof .0063 inch diameter acting as a clamp-free support, the length 1thereof to have a frequency of 164 kilocycles per second is for thefirst mode l=.02'I'I inch.

These illustrative values from Equation 1 indicate approximate nodalpoints on the lead wires 6 and l where the wire 8 or I may be clamped sothatthe mechanical impedance of the wires 6 or I at the crystal I willbe so low that its restriction to the motion of the crystal I will benegligible. The Q of the crystal I will decrease as the lead wireanti-nodes or loops are approached, which occur half-way between thevalues given by Equation 1, and the decrease in Q will be proportionalto the degree of coupling between the two mechanical systemsconstituting the wire system and the crystal I.

Also, as indicated by Equation 1, the proper length of the lead wire 6or I varies inversely as the square root of the frequency, and,accordingly, where the same lead wires 8 and I are used to support acrystal I having more than one effective resonnance frequency, thedistance to the lead wire solder ball It must be a compromise in orderto isolate the supporting system at both the lower and the higherresonances.

The simple fiexure formulas (1) apply in the case of a long thin rod orwire. When the length ".225 centimeter 40 l approaches or becomes equalto or less than the wire diameter, the resonating wire support membermay be designed according to the particular mode of its vibration whichmay be, for example, a shear mode of motion especially in the case ofthe higher frequencies, such as 5 megacycles per second, for example. Inthe case of a wire support soldered to the crystal coating, the theoryof resonating supports is similar to that heretofore discussed but takesinto account also the actual solder cone connection 5 that fastens thewires 6 and l to the crystal I, and the special coupling between thecrystal I and the wire vibrating system.

It will be understood that the solder ball III acts as a clamp for thewires 8 and I and may be placed at any point along the wires 6 and Icorresponding to a wire node. The size or diameter of the solder ballIII need only be sufiicient to act as a clamp, and, in general, the sizewill be in proportion to the wire diameter. The spacing between thesolder ball Ill and the head or top of the cone 5 may be roughlycomputed from Equation 1, or may be determined by experiment. Inpractice, the optimum spacing as determined by test may be found to beslightly greater than that given by the Formula 1, due to the fact thatthe crystal or free end of the wires 6 and I is restricted to a smallslope. The diameter of the solder ball III that acts as a clamp may alsobe determined experimentally by increasing its size or mass until thereare no standing waves on the wires at the side of the solder ball I llremote from the crystal I.

wire supports illustrating the use of a nodal massed weight I in theform of'a soldered wire stirrup II instead of asolder ball III-asillustrated II are as hereinbefore described securely atin Figs. 1, 2,4, -and 6. Except for the substitution of the soldered stirrups Illa, II in place of the solder ball III, Fig. l is similar to Fig. 4 and Fig.8

is similar to Fig. 5 or 6. Fig. 9 shows the hairpin type stirrup ,IIplaced at a node on the lead wire 6 or 1 prior to soldering it theretoby means of the solder mass Ilia ofFigs. 7 and 8. As illustrated inFig.9, th U-shaped copper wire stirrup II may besqueezed or clamped on orover the lead In Flfls. 13 to 16, the massed nodal weights Ilb wires .6and I at or near a node thereof and then, as illustrated in Fig. 7 or 8,soldered thereto on the siderat IIla'away from the crystal I, in' orderto remove the eifects of standing waves in the supportingwires 8 and 8;The crystal I may then be" ground tothe'desiredfrequency andsolderedinto the spring mount wires I ands with little or no changes in thecrystal activity or-frequency.

The U-shaped copper wire stirrup I I may be used to -properly locate andspace the. solder mass Illa ata given distance from the crystal surfaceso that the resulting soldered stirrup" Illa, II is at or 'hereinbeforeI *tached to the wires 6 and I and substantially centered thereon, theline of adhesion to the wires-8 and 'I being clear cut and definite.particularly on'the side thereof that is facing toward the crystal I. I

Figs. 13 to 17 are schematic views illustrating various modifications ofwire supported crystals.

secured upon the crystal support wires 8 and I are illustrated as beingof cubical form although and I. In Figs. 14 and 15, for example, thenodal weights IOb are shown at points on those parts of the wires 8 andI that are remote from the crystal l and removed from the L-bends in thevwires 8 and 1. It will be understood that the weights Iflb are locatedon the support wires in such positions and for the same purposes asherenear a node on thelead wires '8 and, I.- "The U-shaped stirrup IIitself may be composed of soft tempered and having an over all lengthwhen bent into U shape of about V inch, for example. Alternatively, themassed weight Ilia, II may consist of a small copper or otherdisc'threaded ,on and soldered to the lead wires'i'and- I at or near anode thereof.

- Fig. 10 is a perspective view of a crystal mount ing, similar to thatof Figs. 1 and 2, having the laterally extending lead wires 6 and Iterminated in the solder masses III or 10a which form the l solderedjoints between'the lateral lead wires 1 and I and upright spring wires8- and 8. The

upright spring wires 8 and 8 in this instance, as

, shown in Fig. 10, comprisefull elliptical or circu lar-shaped springs,the two'semicircular springs 8 together forming a plane that issubstan-- tiallyiparallel to the plane of the two semicircular springs9. If desired, additional bent springs (not shown) may extend laterallybetween the hou's-' ing I4 and either or both of the springs 8 or 8' forthe purpose of laterally bracing or stabilizing and. damping lateraloscillations in the springs 8 and ill As anvexample, the lateralstabilizing springs for the'spring crystal mounting may consist ofextensions; of'the spring wires 8 and 'I of Figs. 1, 2 and 10, the,spring wire extensions extending outwardly from the solder balls I0 and'then being sprung in bent quarter-circular form .against the oppositeinner side walls of the enclosing cover'or container I4. Such lateral"stabilizing-springs are useful as snubbers' for protection againstshoclr or jar and also for dampening the effects of acoustical resonancewaves' upon the crystalduring operation. Figs;11and'12 illustrate,respectively, face and end views of a four-wire support system asapplied particularly to a longitudinal mode type of i crystali havinglongitudinally'divi'ded platings orcoatings 2a, 2b, 3a, 3b. The fourL-bent spring lead wires 6 and I provide the nodal supports for thecrystal Iand also the individual electrical connections for the crystalI, andin" addition are provided with the massed solder weights III orIlla as hereinbefore described, suit- ;ably spaced from the crystal Ifor the purposes as hereinbefore described. The balls I0 may becomposedof soft solder or of other metal or material and eachmay ordinarilyweigh from, 12 to 20 milligrams ormore, for example. The balls inbeforedescribed in connection with the solder balls I0 and the solderedstirrups IOa. Fig. 17 25, .016 inch diameter tinned phosphor bronzewire,

- reference to particular wire support mountings for particularcrystals, it maybe applied generally to wire supported crystal units,examples of which are given in United States Patent 2,275,122, issuedMarch 3, 1942, to A. W. Ziegler. Although this invention has beendescribed and illustrated in relation to specific arrange- -ments, itisto be understood that it is capable of application in otherorganizations and is, therefore, not to be limited to the particularembodiments disclosed, but only by the scope of the appended claims andthe state of theprior art.

What is claimed is: 1. A piezoelectric crystal mounting comprisin aflexible spring lead wire support attached to andsuspending saidcrystal, a solder ball fastened on said wire support substantially at anode thereof and away from a loop of motion therein, the wire lengthbetween said ball and said crys-' tal being substantially equal to anodd order multiple of a quarter wave-length of said crystal frequencywhereby the natural frequency of said wire length is related to saidfrequency of said i a spring wire for supporting said solder ball.

2.: Piezoelectric crystal apparatus comprisings piezoelectric crystal,asupporting spring wire sei'requencyof said crystal, and means includingI cured to said crystal and flexibly suspending said crystal, and amassed weight suspended on said wire substantially at a node thereofandintermediate the ends thereof, the wire length between said massedweight and said crystal having a natural frequency substantially equalto the frequency of said crystal and means including a bent flexiblespring wire fastened to said first-mentioned wire. on the side of saidweight that is away from said crystal for supporting said weight.

' 3. A mounting for a piezoelectric crystal cornprising crystalsupporting flexible spring lead wires fastened to the crystal andcarried by supports, and a clamp supported by and placed on each of saidcrystal supporting lead wires, said clamps each consisting of a massedweight fastened onto each of said lead wires substantially at a nodalpoint thereof, the length dimension of that portion of each of said leadwires between said weights and the crystal being made of a value torender each of said portions of said lead wires substantially avibrating clamped-free .bar in resonance to the motion transmittedtosaid portions by the crystal, said weights being means for reflectingsaid motion and comprised of suf iicient mass to substantially eliminatesaid motion from the crystal from being transmitted through said weightsto said supports through the remaining portions of said supportingwires, whereby the activity and frequency of the crystal are notappreciably affected by said supporting wires.

4. A crystal mounting in accordance with claim 3 wherein said resonantlead wire portions are substantially coaxial with respect to each other,substantially perpendicular to the major surfaces of the crystal, andfastened to the crystal substantially at points of minimum motionthereof.

5. A crystal mounting in accordance with claim 3 wherein said crystalsupporting wires have substantially coaxial portions and said weightsare placed thereon intermediate the ends of said substantially coaxialportions.

6. A crystal mounting in accordance with claim 3 wherein said resonantwire portions are substantially coaxial with respect to each other, saidremaining wire portions are angularly disposed with respect to saidresonant wire portions, and said weights are placed at the junctionsbetween said resonant wires and said angularly disposed wires.

7. A crystal mounting in accordance with claim 3 wherein said weightsare carried by bent spring wires.

8. A crystal mounting in accordance with claim 3 wherein said weightscomprise a mass of solder on said crystal supporting wires.

9. A crystal mounting in accordance with claim 3 wherein said weightseach comprise a spherical solder ball surrounding a portion of said leadwires.

10. A crystal mounting comprising a face shear mode piezoelectriccrystal element having a nodal point substantially at the center of thecrystal element, metallic coatings formed integral with the major facesof said crystal element, crystal supporting conductive lead wiressoldered to said crystal coatings substantially at the centers of saidmajor faces of said crystal element, spring mounts including bent springwires carrying said lead wires, and a solder mass placed on each of saidlead wires substantially at a node thereof, said mass of solder being ofadequate mass to substantially prevent energy from being transmittedtherethrough to said spring mounts.

11. A crystal mounting comprising a face shear mode piezoelectriccrystal element having a nodal point substantially at the center of thecrystal element, metallic coatings formed integral with the major facesof said crystal element, crystal supporting conductive spring lead wiressoldered to said crystal coatings substantially at the centers of saidmajor faces of said crystal element, spring mounts including bent springwires carrying said lead wires, and a solder mass placed on each of saidlead wires substantially at a node thereof, said mass of solder being ofadequate mass to substantially prevent energy from being transmittedtherethrough to said spring mounts, said lead wires being soldered tosaid spring mounts substantially at said nodes of said lead wires.

12. A crystal mounting comprising a face shear mode piezoelectriccrystal element having a nodal point substantially at the center of thecrystal element, metallic coatings formed integral with the major facesof said crystal'element, crystal supporting conductive lead wiressoldered to said crystal coatings substantially at the centers of saidmajor faces of said crystal element, spring mounts including bent springwires carrying said lead wires, and a solder mass placed on each of saidlead wires substantially at a node thereof and being of adequate mass tosubstantially prevent energy from being transmitted therethrough to saidspring mounts, said solder mass comprising a ball of soft lead-tinsolder.

13. A crystal mounting comprising a face shear mode piezoelectriccrystal element having a nodal point substantially at the center of thecrystal element, metallic coatings formed integral with the major facesof said crystal element, crystal supporting conductive spring lead wiressoldered to said crystal coatings substantially at the centers of saidmajor faces of said crystal element, spring mounts including bent springwires carrying said lead wires, and a massed weight placed on each ofsaid lead wires substantially at a node thereof and being of adequatemass to substantially prevent energy from being transmitted therethroughto said spring mounts, said massed weight comprising a U- shaped copperwire clamped over said lead wires at said node and soldered thereto onthe side away from said crystal element.

- 14. A mounting for a piezoelectric crystal having metallic platings onits opposite major faces, mounting spring wires soldered to said crystalplatings, a solder ball weightplaced on each of said wires substantiallyat a nodal point of said wires, the wire distance between said weightsand said crystal platings being a value to allow said wires to vibratesubstantially as a clamped-free bar. at the crystal frequency, the sizeof said solder ball weights being suflicient to prevent vibration fromthe crystal from being transmitted past said weights, and support wiresfastened at points on said first-mentioned wires on the sides of saidweights that are away from said crystal.

l5. Piezoelectric crystal apparatus comprising a face mode piezoelectricquartz crystal element having conductive electrode coatings formedintegral therewith, a plurality of conductive resilient wire supportsfor said crystal element, each of said wire supports being soldered atone end thereof to one of said crystal coatings adjacent the nodalregion of said crystal element and at its opposite end being carried bya base, each of said wire supports having a mass of solder comprising acast solder ball or globule disposed thereon intermediate said ends ofsaid wire support, the portions of said wire supports between saidsolder masses and said base having bends therein comprising springs,said mass being spaced on said wire substantially at a node thereof, thelength of said wire between said mass and said crystal element being avalue to provide flexure mode vibrations therein of a natural frequencyfor said length of said wire equal to the frequency of said crystalelement, and said mass being of a magnitude suflicient to terminate saidvibrations.

16. Piezoelectric crystal apparatus comprising a piezoelectric crystal,supporting spring wires for said crystal, a sinille massed weightsuspended by each of said wires intermediate the ends thereof, theportions of said wires between said weights and said crystal being tunedto vibrate at a harmonic mode of vibration with a irequencysubstantially equal to the frequency IRVIN E. FAIR.

